Oscillating disc cutters of the type described in international patent specification WO 00/46486 (the contents of which are incorporated herein by way of cross reference) have the general requirement that a mechanism is provided to prevent the cutting disc from rotating at a high speed when the cutter is not engaging the rock face. It should be noted that the reference to international patent specification WO 00/46486 is not an admission that this publication forms part of the common general knowledge in Australia or in any other territory.
In normal cutting mode, when the disc cutter is presented to the cutting face the disc naturally rotates at about 30-40 rpm in the opposite direction to the shaft due to the rubbing friction caused by displacement difference between the diameter of the cutting disc and oscillating path diameter. It will be appreciated that this low speed rotation in the cutting mode is advantageous because it provides for even wear of the cutting disc and prevents temperature build-up at one point on the cutter.
However, during free running mode, when the cutter is not in contact with the rock face, torque transmitted to the disc from the shaft through bearing 609 (shown in FIG. 7 of WO 00/46486 and reproduced here as FIG. 5), causes the disc cutter to rotate in the same direction as the shaft. Without some degree of control, the cutter would speed up to around the same speed as the shaft, i.e. around 3000 rpm.
Reapplying the cutter to the rock face causes an almost instantaneous acceleration of the disc from around 3000 rpm in one direction to around 30-40 rpm in the opposite direction. This can cause significant wear and damage to the cutting edge. In international patent specification WO 00/46486, a solution is proposed of using a gear arrangement shown generally 616 in FIG. 5, (FIG. 7 of that specification).
Such a gear arrangement is heavy, prone to wear, maintenance issues, and causes additional drag when the cutter is engaged with the rock face.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.